A hot-air valve may be used to regulate gas flow in different areas of a gas turbine engine, particularly for aircraft or power generation applications. In certain cases the hot-air valve may have a so called butterfly design, in which a shaft and a disc fixed to the shaft regulate the gas flow through the hot-air valve, particularly by opening and closing a tubular cross-section of a gas line containing the gas flow by a quarter-turn of the shaft. The gas flowing through the hot-air valve may be characterized by a wide temperature range from 219.3 K (−65° F.) to 810.9 K (1,000° F.), and a pressure range from 68.95 kPa (10 psi) to 1.379 MPa (200 psi).
With the objective of rotating the shaft and disc with minimum torque, even under full pressure, the shaft may be supported at each end by a low friction rolling element ball bearing. Each of the low friction rolling element ball bearings may comprise a rotating inner ring fixed to the shaft and a standing outer ring fixed to a housing, with balls as rolling elements in between.
The need for lower fuel consumption of gas turbines, particularly in the aviation industry, has led to a need to operate hot-air valves with higher gas temperatures and higher gas pressures. For example, for an upcoming new gas turbine engine planned to power single aisle, double engine aircraft like the Boeing 737max or the Airbus 320neo, the requirements of the hot-air valve have been increased to a temperature range of 219.3 K (−65° F.) to 977.6 K (1,300° F.) and a pressure of up to 3.103 MPa (450 psi).
Although thermo and mechanical loads have increased in this new application, the size and weight of the valve may not increase, as such would offset the fuel consumption decrease. As a result, all parts of the hot-air valve may be expected to experience larger thermal expansion/displacement caused by the increased temperature range, and larger mechanical deflection caused by the higher pressure and the decreasing stiffness of the valve materials with the increased temperature. More particularly, the shaft may be expected to show more elastic deflection and more linear extension relative to the housing, which has to be compensated by the bearings to avoid the risk of additional internal loads between the bearing elements resulting in a shortened useful life of the bearing.
In light of the foregoing, a need exists in industry to address the aforementioned deficiencies and inadequacies of current low friction rolling element ball bearings, particularly for hot-air valves in aviation applications exposed to the above described increased thermal and mechanical requirements.